Trade ministers from 12 Asia-Pacific nations meeting in Singapore in recent days have edged closer to achieving an ambitious regional pact.

But the end is still not yet in sight for the deal, known as the Trans-Pacific Partnership (TPP), set to cover 790 million people.

The latest round of talks ended in Singapore yesterday with no clear signs of a timeframe as to when the deal will be concluded.

"We made further strides towards a final agreement", the 12 ministers noted in a joint statement yesterday after the four-day talks at the Grand Copthorne Waterfront Hotel.

"We have agreed on the majority of the 'landing zones' identified at our last meeting. While some issues remain, we have charted a path forward to resolve them in the context of a comprehensive and balanced outcome."

However, no date has been set for the next round of negotiations, leaving experts wondering if the deal's conclusion will be reached only near the end of this year.

"Not having any date at all is not a good sign... It makes everyone wonder if they are entering a period of drift," said Dr Deborah Elms, a TPP specialist and head of the Temasek Foundation Centre for Trade and Negotiations at the S. Rajaratnam School of International Studies.

"They didn't get as far as we would have hoped. The progress is not nearly as strong," she told The Straits Times yesterday.

The TPP has been hailed as a cutting edge, 21st-century trade pact that goes beyond removing just tariffs to tackle broader environmental and intellectual property issues. It aims to boost trade, investment and job creation in all the 12 countries.

Singapore's Prime Minister Lee Hsien Loong said in an interview with Chinese media published last week that he was upbeat about being able to close the deal this year.

Yesterday, Singapore's Trade and Industry Minister Lim Hng Kiang told local media: "We're now at the final stage... Out of the seven or eight big issues, the challenges have shrunk because we've resolved some of them. The few remaining ones will have to depend on the final trade-offs."

The TPP talks began in March 2010 with the initial aim of a deal by the end of last year. No new deadline has been set, although it is widely tipped to be concluded this year.

Hopes were high that the talks could be wrapped up by April in time for US President Barack Obama's Asia visit, but experts say this looks unlikely now.

Observers say the momentum could slip away if TPP talks are not concluded by May, as attention shifts towards the US mid-term elections in November.

The central issue of market access is among several main outstanding ones yet to be resolved.

"Market access is in some respects the heart and soul of any trade agreement so until that's done, we don't have an agreement," New Zealand's Trade Minister Tim Groser told reporters.

Australia's Trade Minister Andrew Robb said negotiators had "overwhelmingly broken the back of market access issues" in the Singapore talks, but added that a deal was not yet complete. He said: "My sense is that we are 80 per cent plus there."

Other thorny topics include those on agricultural goods, intellectual property protection and state-owned enterprise.

The TPP nations are: Australia, Brunei, Chile, Canada, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam. These countries account for nearly 40 per cent of the world's economic output and about one-third of all global trade.

They are a massive market for Singapore businesses, with 790 million people and total economic output of about US$28 trillion in 2012. They made up nearly $300 billion, or more than 30 per cent, of Singapore's goods trade in 2012, and include several key trading partners.